The present invention relates to a circuit for extracorporeal blood treatment and the relevant device for flow inversion utilised therein.
It is known that during extracorporeal blood treatment the patient's vascular system is connected to a machine or unit for blood treatment, a dialysis machine, for example.
Connection to the machine creates a circuit in which the blood is drawn from the patient through a needle or other vascular access device connected to the patient itself; the blood is caused to circulate through the unit operating the appropriate treatments on the blood and is then returned to the patient through a return line and a corresponding needle or other access also connected to the patient's vascular system.
The interface between the machine and patient is made up of the vascular access from which the blood to be treated is drawn and to which the treated blood is caused to come back to the human body. It is to be noted that in treatments of the recurring type such as dialytic treatments on chronic patients, a relatively high blood flow in the extracorporeal circuit is required. For the purpose, either needles are used that are fitted in an arteriovenous aneurysm (or shunt) or catheters are used that are implanted into portions of the cardiovascular system where the blood flow is sufficiently high so as to ensure a high drawing capability of the blood to be treated.
It is therefore apparent that a decrease in the performance of the vascular access may represent a serious problem for the patient and therefore the vascular access must be periodically monitored to ensure an optimal functional character of same.
For the above and other purposes some parameters relating to the vascular access are often required to be measured.
One of the different parameters of interest is represented by the real flow passing through the access from which the blood is drawn and then introduced again into the patient's body.
It is in fact apparent that, if due to a degradation of the arteriovenous aneurysm for example (that may be due to the most different causes such as formation of stenosis, collapsing of the vascular walls or others), there is a decrease in the blood flow therein, the dialysis machine will be able to draw a lower amount of blood which will bring about a worsening in the treatment efficiency.
In general, for measuring some of the above mentioned parameters relating to the vascular access, the real aneurysm flow for example, there is a requirement of an inversion between the blood suction point and the blood delivery point at the vascular access.
It is apparent that carrying out this operation manually, i.e. by slipping the respective needles off and inverting suction with delivery in the patient, involves a great trouble for the patient, is time-consuming and as a matter of fact undermines reliability of the measurement of these parameters that are also partly linked to quickness in the inversion.
It is also to be noted that once the blood has been drawn from the patient, it is circulated in a treatment unit that is generally set to enable a counter-current exchange at the inside thereof between the blood to be treated and the dialysis liquid.
In other words, for a good operation of the dialysis machine, maintenance of a hydraulic counter current condition is required within the filtering unit.
To solve the above mentioned problems, appropriate devices to invert the suction and delivery lines at the vascular access have been recently spread, that do not require physical disconnection of the circuit lines for extracorporeal blood treatment from the vascular accesses.
Devices capable of enabling flow inversion at the patient-side suction and delivery branches, while keeping the circulation flow within the filtering unit unchanged have been also developed.
The U.S. Pat. No. 6,308,737 (Krivitski) discloses an inverter device interposed between the vascular access to the patient and the blood pump, and the dialyser capable of enabling a flow inversion in the blood circuit portion directly in communication with the patient's vascular system while keeping the extracorporeal blood flow within the dialyser unchanged.
The inverter in particular comprises a deformable chamber provided with a plurality of doors.
By deforming the chamber along a predetermined direction, a fluid communication between the pre-established doors is created while a fluid communication between other doors is prevented.
In particular, by suitably studying the connections of the extracorporeal blood circuit with the chamber doors and the deformations to be imposed to the chamber itself a flow inversion as above stated is obtained.
The U.S. Pat. No. 5,894,011 (Prosl) too discloses a device for flow inversion in haemodialysis apparatus. This device comprises two discs such interconnected that they can rotate relative to each other without separating. The two discs have appropriate fluid accesses, those of one disc being susceptible of connection with the blood lines directly associated with the patient and those of the other disc being susceptible of direct connection with the bloodlines in fluid communication with the filtering unit.
The two discs can take at least two relative angular positions; in a first position they enable passage of the blood flow in a first direction of direct circulation, in the other position (in which they are rotated relative to each other) they allow an inverted circulation flow in the circuit.
In particular in the second inverted configuration the blood suction line from the patient in the first position becomes the delivery line and correspondingly, the delivery line of the first position becomes the suction line in the second position.
The U.S. Pat. Nos. 6,177,049 and 6,319,465 (Schnell) disclose two further typologies of flow inverting valves both to be positioned between the vascular accesses to the patient and the blood pump and filtering unit.
The first patent teaches use of a fixed external valve body to the inside of which an appropriate insert is connected which is capable of being moved between a first direct-circulation configuration and a second reverse circulation configuration, as shown in FIGS. 1 and 2 of this patent.
In particular, in the second reverse-circulation condition the suction line and delivery line at the vascular access to the patient are inverted with each other with respect to the first direct-flow condition.
The second patent too shows a valve capable of exactly performing the same functions as the first patent, this valve being however made up of two halves coupled with each other so that they have a degree of freedom in rotation and, through mutual rotation of the two halves, a first direct-flow condition and a second reverse-flow condition are obtained at the vascular access to the patient.
A further device for flow inversion in accordance with the U.S. Pat. No. 5,605,630 (Shibata) is also known.
However this device is not used to invert the circulation flow at the vascular accesses to the patient, but to enable flow inversion within the filtering unit. In other words, the blood flow is inverted within the filtering unit intermittently and simultaneously the flow of the dialysis liquid is inverted within the same in such a manner that counter-current conditions are maintained therein. The above is carried out for quite different purposes from those of the present invention, i.e. to avoid blood clotting within the filter for dialysis.
All the patented devices briefly mentioned above however appeared to be susceptible of improvements under different points of view.